The invention relates to water dispersible compositions that are useful for melt sizing textile yarns. The hot melt size compositions are removable from sized yarns by aqueous means.
The art of textile sizing contains many examples of solutions and dispersions of sizes in water and/or organic solvents. Examples of such sizings are shown in U.S. Pat. Nos. 3,546,008 and 3,644,591. The sizing material has generally been applied by passing the yarn through a bath containing the sizing product. The water or solvent is then evaporated. As the yarn is dried, this size will often bond together adjacent ends. The sized ends are then separated mechanically by means of lease rods and combs with the goal of achieving separation of each yarn end from adjacent ends. This separation of bonded warp ends can significantly affect the quality of the size coating resulting in yarn hairiness, reduction in yarn strength, and reduced abrasion resistance.
In an effort to reduce the energy consumption and yarn hairiness, new sizing machines and new sizing compositions have been developed. One class of sizing compositions comprises the hot melt or melt sizes. Hot sizes have several advantages. These include:
(1) Reduced energy consumption. Since there is no water or solvent to be removed from the yarn, the energy required for hot melt application is about 80% less than that needed for conventional aqueous sizing.
(2) Elimination of size cooking and size dumping. There are no sizing solutions to prepare or to dump. A hot melt size can arrive from the sizing supplier in a form ready to use.
(3) Greater speed of application. Since there is no water or solvent to remove, the speed at which the hot melt sizing product can be applied is not limited by drying capacity.
(4) Improved quality of sized warp yarn. Spun yarns, sized by hot melt application with the grooved roll, offer exceptional fiber lay or reduced hairiness.
Several generations of hot melt sizes have been developed. A few examples are known of melt sizes which are based in general upon waxes and other water-insolubles. These sizes do not require removal of solvent during application. However, they often require the use of non-aqueous solvents for removal after the sized yarn has been processed.
Hot melt sizes have been developed which can be removed from the processed yarn by aqueous extraction. One such example is described in U.S. Pat. No. Re. 30,474. The hot melt sizing composition of this patent comprises an intimate combination of a film-forming thermoplastic polymer and a melt-compatible non-polymeric solid modifier and optionally a yarn lubricant. The composition is readily meltable, quick-setting and essentially water- or alkali-soluble. The melt modifier functions to reduce the viscosity of the polymer and to effect an increase in its setting rate. The thermoplastic polymer may be selected from the group comprising water-dispersible or water-soluble linear copolyesters, alkali-soluble acrylic or methacrylic copolymers, meltable and alkali-soluble vinyl acetate copolymers and water-soluble or alkali-soluble phosphate copolymers. The solid modifier may be selected from carboxylic acids, particularly aliphatic dicarboxylic acids, polyhydric alcohols, phenolic acids, polyhydric phenols, and partial esters of polycarboxylic acids.
Hot melt size compositions may be used in various ways. The preferred method of using these compositions involves the utilization of a grooved rotating roller which is heated while a block of the melt size is forced against the roller to be transferred to yarn passing through the grooves of the roller. Such a method is described in U.S. Pat. No. Re. 29,287.
Although hot melt sizes have greatly improved the sizing of textile yarn, it is desirable to develop new compositions which have better processing characteristics. Accordingly, the hot melt sizes of the present invention have improved processing characteristics. The hot melt sizes of the present invention are completely dispersible in water or dilute alkali, possess a low viscosity at lower operating temperatures of 270.degree. F.-300.degree. F., and have a significantly increased heat stability.